Composite filter element

ABSTRACT

A combination filter element comprising a bundle of hollow microporous fibers housed within an extruded carbon block, wherein the carbon block is fabricated to balance particle retention capacity against absorption capacity to provide a composite filter with desirable pressure drop, filter life, and particulate and chemical contamination reduction, and a filtration device, in which combination filter element may be employed, having a base portion including a sump which has an inlet and an outlet and a base which has a reception port for receiving the filter element.

RELATED APPLICATION

The subject application is a continuation application of commonly ownedU.S. patent application Ser. No. 09/300,249, filed Apr. 27, 1999, ofHamlim et al., now U.S. Pat. No. 6,139,739, issued Oct. 31, 2000, whichis a continuation-in-part application of U.S. patent application Ser.No. 09/169,204, filed Oct. 8, 1998, now abandoned, from which priorityis claimed and the specification of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to a composite fluid filter cartridgecomprising a bundle of hollow microporous fibers housed within anextruded carbon block, wherein the carbon block is fabricated to balanceparticle retention capacity against absorption capacity to provide acomposite filter with desirable pressure drop across the cartridge,improved filter life, and desirable particulate and chemicalcontamination reduction.

The subject invention also relates to a fluid filtration apparatus, andmore particular, to a countertop water filtration unit for domestic usein which such composite fluid filter cartridge may find use.

2. Background of the Related Art

Due to run-off and environmental contamination, drinking water in mostareas of the world contains appreciable amounts of dissolved chemicalsand suspended particulate material. A number of chemicals andparticulates that may be found in drinking water have been associatedwith possible adverse physiological effects. Other chemicals andparticulates in drinking water have been associated with less thandesirable taste and sensory perceptions, such as “clouding” of the wateror “souring” of the water. Certain chemicals and particulates in a watersource may lead to undesirable rings in appliances and commodes usinglarge amounts of water, and may result in unsightly films being placedon items washed in the water. In order to reduce particulate andchemical contamination of drinking water, such water is frequentlytreated by chemical processes. Of course, such processes themselves mayintroduce other types of undesirable chemical contaminants into thewater. Chemicals are also not infrequently added to water to act as asanitizing agent, for example, chlorine and bromine. The danger of suchchemicals is only now being questioned.

In the estimation of many persons, municipal water treatment plantsoften fail to adequately deal with these problems. In order to improvewater quality, many residences and businesses now employ on-site waterfilters to improve water streams consumed therein.

Prior Art Fluid Filters

Most systems for improving fluid quality use a series of filters.Filtration is the process of separating particles from a fluidsuspension (liquid or gas) by use of a porous medium or by means of amedium possessing chemical properties, such as hydrophobicity,electrostatic charge, etc., which permit such medium to interact andhold the particles which are to be separated from the fluid whilepermitting the fluid to pass there through. Chemical contaminants areoften removed by filters by means of chemical absorption into, oradsorption onto, the surface of the matter comprising the filter medium.Optimally, it is desired that the filter medium retains most of thesuspended particles and many of the chemical contaminants, but allowsthe fluid being filtered to pass through unimpeded. Flow across thefilter medium is generally achieved by the application of a drivingforce, usually in the form of a pressure difference across the filter,which may be generated, for example by external pressure appliedupstream, a vacuum applied downstream, gravity, or other force.

Fluid filters are often of such dimensions or fabricated in a construct,so as to form relatively rigid replaceable filter units or “filtercartridges.” Filter cartridges often employ granular activated carbonelements in their construct. Granular activated carbon is useful forremoving organic chemicals such as chlorine, hydrogen sulfide,pesticides, herbicides, phenol, chlorophenol and hydrocarbon from water.Other filter elements may be employed in the cartridge construct tohelp, for example, to remove sediments such as rust and other particles.Silver is sometimes impregnated into one or more filter element toinhibit bacterial growth. Ion exchange resins may also be employed.

While filter cartridges containing granular activated carbon are knownto be good at removing contaminants that affect taste, odor of thefiltrate, and visible particulate matter, such filter cartridgesgenerally are not fine enough to remove bacteria or viruses. Water maybe contaminated with a number of micro-organisms including pathogenicbacteria, amoebae, flagellates, viruses and protozoa. In fact, as somewater remains inside carbon granules after filtration, stagnant water inthe carbon granules may act as a breeding ground for micro-organisms.Therefore, water discharged after a long period of non-use of acarbon-based filter cartridge may be contaminated with living organisms.

Recognizing that prior art filter cartridges which incorporate only asingle filter medium, in particular a carbonaceous medium, suffer fromthe inability to remove many of the contaminants found in water, therehave been developed filter assemblies employing a plurality of filtermedia, such as disclosed in U.S. Pat. No. 5,188,727. For example, inU.S. Pat. No. 4,828,698 there is disclosed a filter assembly having anouter cylindrically-shaped filter structure with porosity such as to beremove particulate matter, a inner cylindrically-shaped sorbantstructure for sorbing chemical contaminants, and an inner-mostcylindrically-retained microbiological filter, preferably comprising amicroporous membrane for removing microorganisms, surrounding aperforated core housing a central void. By moving water across from theouter structure to the central void, particulates are removed, chemicalsare adsorbed or absorbed, and microorganisms are filtered out.

Numerous microporous filter elements are utilized in the art to removebacteria, viruses and other micro-organisms. Among these elements arehollow fibers having micropores coursing through the fiber walls. Asdisclosed in U.S. Pat. No. 3,526,001 (the disclosure of which isincorporated by reference herein), hollow selectively permeable fibersfor use in filtration have been known for several years. Typicalmicroporous hollow fibers include Celgard™ manufactured by the Questardivision of Celanese Corporation. Such hollow fibers offer controlledand relatively uniform porosity as compared to many asymmetricultrafiltration and microfiltration membranes. Fiber construct is suchthat there is high membrane surface area-to-volume ratio. The pores inthe fibers form tortuous, interconnected channels leading from onesurface of the fiber to the other. The pores of these hollow fibersallow the flow of fluid but block passage of many bacteria, colloids andother sub-micron particles. Fibers having pores of 0.05 microns or lessare capable of filtering most viruses. In order to assure passage of thefluid through the fiber pores rather than through any end, such fibersare generally potted in an epoxy or other standard potting material atboth ends of the fiber in a manner that the openings at both ends remainopen.

Microporous hollow fibers have been mounted within filter cartridges innumerous ways including: placing them rectilinearly in the cartridge(e.g., U.S. Pat. Nos. 4,334,993, 5,041,220, 5,554,283), winding themabout a cylindrical support (e.g., U.S. Pat. No. 4,045,851), andbundling them in a U-shape (e.g, U.S. Pat. Nos. 5,032,269 and5,225,079). By judicious selection of hollow tubule lengths, asdisclosed, for example, in U.S. Pat. No. 5,032,269 (the disclosure ofwhich is incorporated by reference herein), a U-shaped bundle ofmicroporous hollow fibers aids in maximizing filtration surface area,and thus filtration efficiency, while providing ease of manufacture andplacement of the fibers in sealant material.

U.S. Pat. No. 4,636,307 discloses a filter unit housing particulategranulated activated carbon surrounding a bundle of U-shaped poroushollow fibers. Such system is said to aid in both removing chemicals andimpurities from the filter water, as well as micro-organisms. While suchsystem improves water filtration, use of mobilizable carbon particles inits construct can be said to suffer from several disadvantages, amongthese the settling of the particles over time leading to decreasedfiltration efficiency, and channeling of filtrate in the sorbant bed dueto unintended shock or vibration leading to a decrease in thereliability of the filtration system. Further the disclosed embodimenthousing the U-shaped porous hollow fibers within the housing granulatedactivated carbon indicates a housing about the fiber bundlesignificantly reducing radial flow through the fibers, and consequentlyleading to increased pressure drop across the unit and reducedfiltration rate.

U.S. Pat. No. 5,102,542 discloses a canister-type filter comprising acarbon block or molded carbon block surrounding or operatively connectedto a recti-linear bundle of porous hollow fibers housed within a flowcontrol tube. The flow control tube is disclosed to be comprised ofresin material and to be positioned about the porous hollow fiber bundlepreferably for approximately 70% of the bundle's length. The flowcontrol tube is said to force water to take a longer path through thecarbon block, thereby improving filtration. While use of the carbonblock permits filtration without the problems associated with settlingof the sorbant or channeling of the filtrate in the sorbant, the filterof U.S. Pat. No. 5,102,542 suffers from drawbacks that make use of suchfilters less than desirable. First, the described filter assemblies,owing in part to employment of a flow control tube, require high fluidpressures for filtration and result in high fluid pressure drop in thefiltration process. While filtration through the carbon medium may besaid to be improved by increasing the path of flow through the medium,this reference fails to take into account that filtration rateefficiency across the porous hollow fibers and filtration life of theassembly is significantly reduced by reduction of the exposed surfacearea of the fibers available for radial filtration. Rectilinear pottingof the microporous hollow fibers further adversely impacts on thefiltration flow rate by failing to maximize surface area exposed to theincoming filtrate.

There is a need, therefore, for an improved filtration assembly whicheffectively reduces both particulate mass and chemical contamination ina fluid stream, which affords adequate filter life and provides forconsistent filtration quality relatively unaffected by the age of thefilter or by ordinary handling of the filter unit.

Prior Art Fluid Filtration Units

Until relatively recently, most on-site water filters were typicallydesigned to be mounted in a permanent housing coupled to a water stream,such as in series with a pipe. Such permanent housings were oftenlocated in relatively poorly accessible locations (such as under a sinkor in the basement) and often required special tools in order to gainaccess to the filter residing in the housing (such as a wrench). Whileon-site permanent filters are often perceived to remediate the watersufficiently for everyday uses, such as washing dishes and clothes,there is a large and growing number of people who demand cleaner andmore tasteful water for internal consumption. Rather than adding newtypes of filters into permanent-type on-site water filter housings orincreasing the number of such housings, in order to provide for a moreconvenient manner of coupling filters to water streams and of changingfilters, so-called “countertop filtration units” were developed.“Countertop filtration units” are portable filter apparatusesdimensioned to fit on a standard household countertop and adapted forcoupling to a fluid flow outlet spigot, such as a faucet. Such units aregenerally intended for domestic use to filter impurities out of tapwater. The unit may be placed on a counter adjacent to a sink.

Countertop filtration units are generally fabricated from plastic and/ormetal. Conventionally, these units comprise a base upon which a “sump”,such as a cup or cover, which acts as a sump, is placed and in which thefilter cartridge is housed. The “sump” is generally screwed into thebase wherein a seal typically exists to permit fluid tight sealing. Thefilter in conventional counter filtration units is changed by removingthe “sump”, pulling out the spent filter, inserting a new filter intothe “sump” and reattaching the same to the base. The “sump” has an inletopening to enable an entrance of the fluid into the “sump” and throughthe filter materials. The “sump” further has an outlet opening to enablethe fluid to be discharged from the “sump” after it has coursed throughthe filter. The unit may filter be equipped with a valve to selectivelydivert the fluid flowing to the filter cartridge.

Filters used in countertop filtration units are designed to bedisposable. One commonplace type of disposable filter is in the form ofa solid porous cylinder having a hollow center. When such filters areemployed, the fluid to be filtered flows radially through the wall ofthe cylinder. between its exterior and hollow core. Such filters aregenerally capped at each end with a boundary sealing-cap to permitsealing between the filter and the housing in which it is placed in sucha manner as to assure that only fluid having passed through the wall ofthe filter cylinder and into the hollow core is permitted to exit fromthe filtration unit.

Typically, countertop filtration units employ filters fabricated fromgranular activated carbon. As noted above, while carbonaceous filterelements are known to be good at removing contaminants that affecttaste, odor of the filtrate, and visible particulate matter, suchfilters generally are not fine enough to remove bacteria or viruses.

Countertop filter cartridges conventionally can be classified as beingeither of two types: encapsulated and drop-in. Encapsulated cartridgesincorporate the “sump”, such that the “sump” must be replaced with thefilter element. The advantages of encapsulated cartridges are that theyare user friendly and the seal between the base and “sump” are replacedeach time. There also are advantageous to manufacturers in that theygenerally require proprietary cartridge replacement. Drop-in cartridgeson the other hand are replaced independently of the “sump”, the “sump”being re-used each time. The advantage of the drop-in cartridges overencapsulated cartridges is that such cartridges are generally cheaper.

There are problems associated with countertop filtration units employingeither encapsulated or drop-in filter cartridges. Both systems requireremoval of the “sump” from the unit in order to replace the filter.Removal of the “sump” from the base is often less than convenient, giventhat the “sump” is generally screwed into the base by means ofrelatively large threads. Further, as most countertop filtration unitshouse the “sump” in an external housing, designed in part to hide therather non-aesthetic “sump” and inflow/outlet tubes, the externalhousing must also be removed before access to the “sump” may be had. Asthe process involved in removing and changing either encapsulated ordrop-in filter cartridges is relatively complex, fluid filtrationquality often suffers due to less than optimal replacement of thefilter. In regard to “drop-in filter cartridges” such filters suffer notonly from the problems associated with ease of access to, andreplacement of the filter element, but also with respect to the need tocontinually replace the seal between the “sump” and the base. On theother hand, “encapsulated cartridges,” due to the inherent cost of the“sump” which is replaced with each filter change, can be far less thaneconomic.

There is a need, therefore, for an improved countertop filtration unitwhich permits easy replacement of filter elements and aids in assuringadequate sealing between the “sump” and base.

SUMMARY OF THE INVENTION Novel Fluid Filter Elements

The present inventors have resolved many of the problems associated withprior art filter assemblies, particularly those of the cartridge-type,by employing a composite filter medium comprising a carbon-based filtermedium to remove particulates and to absorb chemical contaminants, andmicroporous hollow fibers, or other microporous filter elements, forremoval of micro-organisms. The present inventors have discovered thatby using a carbon block surrounding a bundle of microporous hollowfibers (preferably the bundle being in a U-shape) wherein radial flow ispermitted along the greater part of the surface area of the hollow fiberbundle that a desirable blend of utilization life, filtration rateoutflow, and pressure differential across the filter assembly can beachieved, without significantly affecting the quality of the filteredfluid (in particular as compared to prior art embodiments employing bothmedium for purposes of filtration). In particular, the present inventorshave discovered that by balancing the chemical sorptive properties ofthe carbon block against the pressure drop across the block, that acarbon block/microporous hollow fiber filter assembly can be preparedwith significantly improved properties over the prior art. Suchimprovements considerably advance the art, and argue against the priorart teaching of the need for output restricting flow control tubes, andthe like, to be placed over the majority of the surface area of amicroporous hollow fiber bundle when a carbon filter medium, inparticular a solid carbon block, is used as a pre-filter.

When designing a filter it is desired to have as low as possible apressure differential across the filter unit, as the larger the pressuredrop across a filter unit, the more energy is needed to move fluidthrough the filter unit for the same filtration rate. It is alsodesirable to optimize as much as possible the sorbant activity of thefilter medium in order to efficiently remove solubilized chemicalcomponents from the fluid being filtered. It is yet further desired thatfluid filtration rate be high enough to provide adequate filtered fluidper unit time. And, of course, it is yet further desired thatimprovement of any, or all, of these factors not affect the quality ofthe product produced by the filtration process. Failure to account forany of these factors may result in a commercially-unacceptable product.

As would be recognized by one of skill in the art, balancing of each ofthe above factors is particularly difficult given the many competingparameters involved. For example, both pressure drop and adsorption rateare strongly influenced by particle size. Unfortunately, a change inparticle size and particle size distribution has opposite effects onthese two factors. Resistance to fluid flow is inversely proportional tothe void spaces in a packed bed of particles. Therefore, small particlesizes typically increase resistance to fluid flow and cause a highpressure drop. Adsorption, on the other hand, which typically is greatlyaffected by the mass transfer resistance of the particles (a measure ofadsorbate transport from the bulk fluid phase to the internal surfacesof the adsorbent particles), generally is greatly increased by reducingparticle size. When mass transfer resistance is reduced, the masstransfer zone is correspondingly reduced (i.e., a long mass transferzone is typically caused by a large mass transfer resistance), thusgenerally substantially increasing the efficient operation ofadsorption/desorption cycles. A long mass transfer zone, which generallyentails a large quantity of partially utilized absorbent, will result ina short adsorption step and inefficient use of the adsorbent capacity.The mass transfer transport rate is dominated by two mass transfermechanisms in series: (a) interfacial mass transfer, that is, diffusionthrough the fluid boundary layer surrounding the external surface of theadsorbent particle; and (b) intraparticle mass transfer-diffusionthrough the internal pore space (micropores and macropores) of theparticle to its interior surface where adsorption can take place. Inshort, small particles offer large fluid/solid contact areas in thefixed bed for interfacial mass transfer and reduce the path length forthe intraparticle diffusion. Sorption kinetics are also typicallyimproved by small particle size. Sorption, of course, is also affectedby the composition of the sorption particles.

In a similar fashion, an increase in fluid flow rate typically reducessorption of solubilized contaminants. Such is due to the fact thatincreased fluid flow rate reduces the time in which the fluid to befiltered is allowed to remain in contact with sorbant material. As eachtype of particle differs in the rate at which adsorbate is transportedfrom the bulk fluid phase to the internal surfaces of the sorbantparticles, increased flow above a certain rate may significantlydecrease the probability that sorption will occur before the fluidleaves the filter. If the rate of fluid flow is too high, adequatefiltration is not achieved. Fluid flow rate may also be affected in anopposite manner than sorption rate based on the composition of thesorption particles.

Prior art filter elements which attempt to reduce both particulatecontamination, dissolved chemical contamination, and micro-organismssuffer from a number of deficiencies. Many of these filter elements useparticle-packed housings as a pre-filter to a microporous membranefilter. Such filter elements suffer from an inherent capacity offreestanding particles to repack within the housing. Re-distribution ofparticles, in particular packing, can lead to decreased filtrationquality. Further, channeling within the particle bed can also adverselyaffect filter fluid quality. Combination filter elements which attemptto overcome this problem by featuring a sorbant containing structure inwhich the sorbant material is immobilized, such as in U.S. Pat. No.4,828,698, suffer from a relatively low surface area proffered by themicroporous element to the fluid which has passed through the sorbantfilter element. The relatively low surface area causes an increase influid pressure across the unit, and leads to more rapid clogging of themembrane filter (and thus lower filter unit life expectancy).

Combination filter elements have been developed which attempt to replacethe membrane filter with other microporous filter elements, such asmicroporous hollow fibers. Generally such combination filter elementsare placed in spacial seriatim from each other, one on top of the other,thereby requiring a separate housing following the particulate/sorbantpre-filter and, therefore additional cost in filter unit fabrication.Certain combination filter elements, however, place the microporousfilter element within the particulate/sorbant pre-filter. Prior artfiltration assemblies of such construct are, unfortunately, far fromoptimal.

U.S. Pat. No. 5,102,542 teaches use of a carbon block rather thangranulized particles in a housing, thereby reducing the possibility ofdecreased filtration quality due to re-distribution of particles andremoving the need for a special housing to house the particle. However,the patent further teaches use of microporous hollow fibers in anon-surface area optimizing rectilinear formation surrounded along thegreater part of the length of the fibers by an impermeable flow controltube. The tube is placed along the fibers in order to improve filtrationby forcing at least a part of the fluid to take a longer path throughthe carbonaceous filter. Such control tube, however, leads tosubstantially increased fluid pressures across the unit of a given flowrate (reduces the fluid flow rate for the same pressure differential),and reduces significantly the amount of the microporous filter that canbe incorporated into the design. Further, by restricting axialfiltration into the microporous filter element, fluid flow rate throughthe unit is significantly reduced.

U.S. Pat. No. 4,636,307 discloses a U-shaped microporous hollow fiberbundle within a housing containing granulated particulate material.While the U-shaped bundle increases surface area over a rectilineararrangement, U.S. Pat. No. 4,636,307, like U.S. Pat. No. 5,102,542, alsoteaches that the greater part of the linear length of the bundle becovered in an impermeable covering (See, e.g., FIG. 10). The patentfurther fails to consider the problem of particulate packing andchanneling that not infrequently occur with particulate-packed housings.

The present inventors have overcome the drawbacks of such prior artcombination filter elements by housing a significantly unsheathedmicroporous, hollow fiber bundle, preferably in a U-Shape, in a carbonblock. The inventors have particularly discovered that by carefullyadjusting the particle size and construct of the carbon block, so as tobalance mass transfer resistance (and thus chemical sorptive activity)against desired pressure drop, that a highly efficient combinationfilter unit utilizing carbon for particulate removal and sorptivechemical reduction, and microporous hollow fibers for removal ofmicro-organisms, can be constructed without unacceptable pressure dropacross the filter unit and without the need for substantially limitingquantity of fibers, and size of the fiber bundle, available for radialfiltration (thereby reducing filtrate rate). Such construct provides amuch more robust filter unit then those constructs previously available,without the drawbacks of unacceptable pressure drop across the filterunit, unacceptable fluid filtrate clearance through the unit,unacceptable filtrate quality, and additional parts in the construct ofthe filter unit. The inventors have further discovered that by adding amore open porous pre-filter outside of the carbon block that the purityof the filtrate can be even more improved without adverse effect onpressure across the filter and filtrate clearance rate.

An embodiment compound filter cartridge of the present invention, usefulfor filtering fluids, comprises a carbonaceous filter block elementsurrounding a void wherein the carbonaceous filter element has a fluidentry port located proximal to an outer portion of the carbonaceousfilter element, and a selectively permeable fiber bundle positioned inthe carbonaceous filter element void for receiving fluid which passesthrough the carbonaceous filter element into the carbonaceous filterelement void. Preferably, the carbonaceous filter element is defined atleast in part by an extruded carbon block, but can also be defined inpart by a molded carbon block, or formed in part by means ofwet-felting, dry-felting and a variety of other techniques. Preferably,the fiber bundle comprises a plurality of hollow, microporous fiberseach having a first open end and a second open end. Preferably, thefirst and second open ends are potted in a sealing compound such thatthe first open end and the second open end of each of the hollow fibersare exposed on an outer end face of the sealing compound body permittingfluid entering the hollow, microporous fibers to exit through said outerend face of said sealing compound body. Preferably, less than about 60%of the selectively permeable fiber bundle is sheathed from axial flow.

Another compound filter cartridge embodiment of the present inventioncomprises a carbonaceous filter element surrounding a void wherein thecarbonaceous filter element has a fluid entry port located proximal toan outer portion of the carbonaceous filter element; a cage positionedin the carbonaceous filter element void, and a selectively permeablefiber bundle positioned in the cage for receiving fluid passing throughthe carbonaceous filter element into the carbonaceous filter elementvoid. Preferably, the carbonaceous filter element is defined at least inpart by an extruded carbon block, but can also be defined in part by amolded carbon block, or formed in part by wet-felting, dry-felting and avariety of other techniques Preferably, the fiber bundle comprises aplurality of hollow, microporous fibers each having a first open end anda second open end. Preferably, at least one open end is potted in asealing compound, anterior to the cage and the carbonaceous filterelement, such that the open end is exposed on an outer end face of thesealing compound body permitting fluid entering the hollow, microporousfibers to exit through said outer end face of said sealing compoundbody. Preferably, the cage has sufficient openwork such that more thanabout 40% of the surface area of the selectively permeable fiber bundleis in direct contact with fluid when fluid fills the carbonaceous filterelement void.

And yet, another compound filter cartridge embodiment of the presentinvention, which is useful for filtering fluids, comprises: acarbonaceous filter element surrounding a void approximately concentricwith a central axis of the carbonaceous filter element, the carbonaceousfilter element having a fluid entry port located proximal to an outerportion of the carbonaceous filter element; a perforated jacketpositioned in the carbonaceous filter element void in a mannerapproximately concentric with the central axis of said carbonaceousfilter element, and a selectively permeable fiber bundle positioned inthe perforated jacket for receiving fluid passing through thecarbonaceous filter element into the carbonaceous filter element void.Preferably, the carbonaceous filter element is defined at least in partby an extruded carbon block, but can also be defined in part by a moldedcarbon block, or formed in part by wet-felting, dry-felting and avariety of other techniques. Preferably, the fiber bundle comprises aplurality of hollow, microporous fibers each having a first open end anda second open end. Preferably, at least one open end is potted in asealing compound such that the open end is exposed on an outer end faceof the sealing compound body permitting fluid entering the hollow,microporous fibers to exit through the outer end face of the sealingcompound body. Further, it is preferred that the perforated jacket hassufficient perforations such that more than about 40%, more preferably,more than about 50%, and yet more preferably, more than about 70% of thesurface area of said selectively permeable fiber bundle is in directcontact with fluid when fluid fills said carbonaceous filter elementvoid.

And, there is disclosed a compound filter cartridge embodiment forfiltering fluids comprising: a pre-filter element, for filtering courseparticulates, surrounding a void, the pre-filter element having a fluidentry port located proximal to an outer portion of the pre-filterelement; a carbonaceous filter element positioned in the pre-filterelement void, the carbonaceous filter element surrounding a carbonaceousfilter element void, and a selectively permeable fiber bundle positionedin the carbonaceous filter element void for receiving fluid passingthrough the pre-filter element and carbonaceous filter element into thecarbonaceous filter element void. Preferably, the fiber bundle comprisesa plurality of hollow, microporous fibers each having a first open endand a second open end. Preferably, the carbonaceous filter element isdefined at least in part by an extruded carbon block, but can also bedefined in part by a molded carbon block, or formed in part bywet-felting, dry-felting and a variety of other techniques. Preferably,the first and second open end are potted in a sealing compound in such amanner that the first open end and the second open end of each of saidhollow fibers are exposed on an outer end face of the sealing compoundbody permitting fluid entering the hollow, microporous fibers to exitthrough the outer end face of the sealing compound body. Preferredpre-filter material includes polypropylene, polyester, and various othernon-woven material, cellulosic, glass, or other sheet-like filtrationmediums.

Novel Countertop Filtration Unit

The present invention further provides an improved countertop filtrationunit which provides user-friendly filter cartridge replacement and aidsin assuring adequate sealing between the sump and base. The presentinvention provides a countertop filtration unit having a sump integralwith the unit's base, the base having a reception port for filterelement engagement into, and disengagement out of, the sump.

By “sump” it is meant any reservoir serving as a receptacle for liquidswhich is constructed so as to able to withstand the fluid pressures towhich it is exposed. By “base” it is meant any housing on which the sumprests and which is designed to typically interface with the surface uponwhich the filter unit is to be placed. By “reception port” it is meantany communication area positioned in the base permitting reception of afilter cartridge into the area and out of the area. By “end-cap” it ismeant a substantially solid piece of material placed at the end of afilter element which is dimensioned so as to at least seal the greaterportion of the surface area of an end of the filter element. By“adapter” it is meant any structure for joining one element to another.By “fluid adapter,” it is meant a structure for allowing communicationof a fluid stream with the filter element, typically by means of fluidconduits, such as tubing. By “filter element” it is meant anycombination of materials used to filter out suspended or dissolvedparticles or chemicals from a fluid. By “microporous hollow fibers” itis meant an elongate structure having a central void constructed such tohave a relatively high membrane surface area-to-volume ratio and porouswalls wherein the pores of the wall lead from one surface of the fiberto the other surface of the fiber and are substantially of such size asto be able to block the passage of submicron particles and organisms. By“external housing” it is meant any housing for surrounding and enclosingthe sump. By “inlet” it is meant an opening for intake of fluid, whereasby “outlet” it is meant an opening for the out-take of fluid.

One embodiment of the present invention includes a filtration unit whichcomprises a base portion including a sump for accommodating a filterelement and a reception port for receiving the filter element. The sumphas an inlet and an outlet. Preferably the reception port is defined ina bottom surface of the base portion. The unit may further include anexternal housing portion for engaging the base portion to enclose thesump. Preferably the end cap includes a camming surface for cooperatingwith a complementary surface in the base portion to facilitateengagement and disengagement of the end cap and the reception port.

Preferably, the filtration unit has the sump integral with the baseportion, and the reception port is defined in a bottom surface of saidbase portion. Preferably, the filter element to be received in thereception port is dimensioned and configured for accommodation withinsaid sump, and is constructed so as to have an end cap dimensioned andconfigured for engaging the reception port. The end cap may include acamming surface for cooperating with a complementary surface in saidbase portion to facilitate engagement of the end cap and the receptionport. Preferably, a first seal is associated with either or both thereception port and the end cap so as to effect a seal between the endcap and the base portion. A second seal may further be associated witheither one end of the filter element and/or the interior surface of thesump to effect a seal between said filter element and the sump. Thefilter element may be defined at least in part by an extruded carbonblock or by hollow microporous fibers. Preferably, the filter element isa composite filter element including first and second filtration media,wherein the first filtration media comprises an extruded carbon blockand the second filtration media comprises hollow microporous fibers.

Still another embodiment of the present invention includes a filtrationdevice which comprises a filter element having an end cap provided at afirst end thereof, a base portion including an integral sump foraccommodating the filter element and a reception port for receiving thefilter element and engaging the end cap; and a housing portion forengaging the base portion to enclose said sump.

In a preferred embodiment the sump is formed monolithically with thebase portion. It is preferred that the reception port be defined in abottom surface of the base portion. While the end cap may be engaged tothe base by any of the many attachment mechanisms known in the art, inone embodiment, the end cap includes camming lugs for cooperating with acomplementary camming surface in the base portion to facilitateengagement of the end cap and the reception port. It is preferred that afirst seal be associated with at least either the reception port and/orthe end cap to effect a seal between the end cap and the base portion. Asecond seal may be associated with at least one of an end portion ofsaid filter element and an interior surface of the sump to effect a sealbetween the filter element and the sump. The filter element may bedefined at least in part by an extruded carbon block or by hollowmicroporous fibers. Preferably, the filter element is a composite filterelement including first and second filtration media, wherein the firstfiltration media comprises an extruded carbon block and the secondfiltration media comprises hollow microporous fiber.

And yet another embodiment of the present invention includes a filterdevice for housing a filter element having an end cap associated with anend thereof, which comprises a base portion for accommodating the filterelement, the base portion being integral with a sump having an inlet andan outlet, wherein the base portion encompasses a void through which thefilter element may be positioned in said sump, and the base portionsurrounding said void includes an engagement surface complementary tothe surface of the end cap for engaging the filter element; and ahousing portion for engaging the base portion to enclose the sump.

These and other unique features of the combination filter element andfiltration system disclosed herein will become more readily apparentfrom the following description, the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the disclosedcombination filter element and filtration system appertains will morereadily understand how to make and use the same, reference may be had tothe drawings wherein:

FIG. 1 is a perspective view of a countertop filter unit coupled to anadapter assembly for attaching the filter unit to a fluid stream;

FIG. 2 is a perspective view of a filter unit and filter cartridgeassembly embodiment of the present invention;.

FIG. 3 is a perspective view of an end-cap for engagement into the baseportion of the filter unit assembly of FIG. 2;

FIG. 4 is a cross-sectional view of the end-cap of FIG. 3 cut along axis4—4;

FIG. 5 is an interior perspective view, partly in section, of a filterelement end-cap/base coupling mechanism of an embodiment of the presentinvention;

FIG. 6 is a cross-sectional view of the assembled filter unit embodimentof FIG. 2;

FIG. 7 is a perspective view of the assembled filter cartridge of FIG.2; and

FIG. 8 is a perspective view of a filter cartridge assembly embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION Novel Fluid Filter Element

The above described filter unit preferably employs a combination filterelement incorporating activated carbon bound into block by binders. Theuse of a carbon block aids in providing rigidity to the filterstructure, overcomes the need for an external housing, as well assubstantially eliminates the possibility of channeling andre-distribution of carbon particles, and permits the bed structure toremain stable throughout its service life. The carbon block is used tosurround a significantly un-sheathed microporous hollow fiber bundlewhich preferably is in a U-Shaped form to optimize the surface areaavailable to radial filtration.

By recognizing the importance of optimizing the balance between sorptiveactivity and pressure drop across the carbon block, the presentinventors have overcome the need to employ control flow tubes whichsheath the greater part of microporous hollow fiber bundles, as found inprior art combination filter assembly embodiments. Removal of suchcontrol flow tubes permit greatly improve filtration rate, increase thein-line life of the filter unit and permits more efficient radial flowinto the fibers. The inventors have discovered that by carefullyadjusting the composition of the carbon block to minimize pressure dropper unit change measured in air flow resistance across the carbon block,superior carbon block compositions may be developed for use in filterunits employing a carbon-based particle retention/sorptive filterelement and microporous hollow fiber element. Such filter unitssignificantly exceed the filtering characteristics of similar prior artconstructs.

The air flow resistance (AFR) per depth of filter media (d) may becalculated via the equation: ΔP/d=k F/A wherein k is a constant, F isthe flow rate of the fluid passing through the filter media and A is thefilter area through which the fluid being filtered passes. The presentinventors have discovered that carbon blocks having a “k-value” (whichis represented by the slope of a plot of pressure drop per unit depth(e.g. inch of H₂O/inch filter traversed) versus rate of air flux (e.g.,SCFH/ft²)) of between about 0.01 to about 0.10, more preferably betweenabout 0.02 to about 0.07, and yet more preferably between about 0.03 toabout 0.05, demonstrate superior adsorption capacities without anunacceptable reduction in fluid flow rate, or a need for increasedpressure to retain fluid flow rate. The filter unit life of carbonblock/microporous hollow fiber assemblies has also been shown to bemarkedly enhanced when the carbon block has a k-value between theseranges. As would be known to one of ordinary skill in the art, the“k-value” typically has units of$\frac{\left( {{in}\quad H_{2}O} \right)\quad \left( {ft}^{2} \right)}{{{in}.\quad {media}}\quad ({SCFH})}.$

Novel Countertop Filtration Unit

The present invention further overcomes many of the prior art problemsassociated with countertop filtration units. There is provided asignificantly improved countertop filtration unit which allows foruser-friendly filter cartridge replacement, as well as aiding inassuring adequate sealing between the sump and base. The presentinvention provides a countertop filtration unit having a sump integralwith the unit's base, the base having a reception port for filterelement engagement into, and disengagement out of, the sump.

Representative Illustrations of the Present Embodiments

The advantages, and other features of the novel combination filterelement and novel countertop filtration unit, in which such elementsfind particular usefulness, will become more readily apparent to thosehaving ordinary skill in the art from the following detailed descriptionof certain preferred embodiments taken in conjunction with the drawingswhich set forth representative embodiments of the present invention andwherein like reference numerals identify similar structural elements.

Referring to FIG. 1, there is shown a perspective view of a countertopfilter unit 10 coupled through one or more conduits 18, 20 to an adapterassembly 16 for attaching the filter unit to a fluid stream. Countertopfilter unit 10 includes a base 14 on which is mounted an externalhousing 12, base 14 and external housing 12 defining the exterior ofcountertop filter unit 10. Adapter assembly 16 is designed to beconnected to fluid flow, as from, for example, a sink, by means ofconnector 26. Fluid flow entering the adapter through connector 26 maybe directed to countertop filter unit 10 by way of conduits 18, orthrough direct throughput opening 24 in adapter 16, by stopcock 22.

Now referring to FIG. 2, there is shown a perspective view of a filterunit assembly embodiment of the present invention. Base 14 includes sump32 which is dimensioned to fit a filter cartridge, generally designatedin its component parts as 50. Sump 32 is shown to have inlet and outlet,28 and 30, for admitting to, and removing from, sump 32 fluid. Inlet 28and outlet 30 are connected to the exterior of filter unit 10 throughconduits 20 and 18, respectively. Sump 32 is generally surrounded bycover 12 and may be connected to the same through connecting structure,such as, but not limited to, screws 36 and threaded receptacles 34. Afirst panel 38 may be positioned over screws 36 to provide for a moreaesthetic cover 12 exterior. Cover 12 may further house therein a powersource 40 for powering any electronics associated with the filter, suchas a timing clock (not shown) to indicate whether filter change isrecommended. A second panel 42 may be positioned over power source 40 toprovide for a more aesthetic cover 12 exterior. Base 14 may be equippedwith stand-offs 74 (See FIG. 5).

Filter cartridge 50, or any other filter cartridge adapted to sealinglyfit within sump 32, may be utilized in countertop filter unit 10. Filtercartridge 50 is comprised of two filter elements, one comprising ajacket of carbonaceous material, 44, the other comprising a U-shapedbundle of hollow, microporous fibers 48 as a preferred embodiment. Thejacket of carbonaceous material 44 may be formed by an extrusionprocess. Hollow, microporous, fiber bundle 44 is housed concentricallywithin the cavity 56 formed by carbonaceous jacket 44. Hollow,microporous, fiber bundle 48 is formed by potting hollow, microporousfibers in the bottom portion of upper cage 82 (See FIG. 8). Upperend-cap 52 has a sealing neck 62 for sealingly connecting to internalsump collar 78 as shown in FIG. 6. Sealing neck 62 preferably is fittedwith upper seal 54 to aid in complete sealing between sealing neck 62and internal sump collar 78. Filter cartridge 50 is further fitted witha lower end-cap 46.

As shown in perspective view in FIG. 8, the U-shaped bundle of hollow,microporous fibers 48 may be contained in a cage 82, cage 82 and hollow,microporous fibers being pulled in upper end-cap 52. Cage 82 ispositioned within cavity 56 formed by carbonaceous jacket 44.

As shown in perspective view in FIG. 3, and in cross-sectional view inFIG. 4 (along 4—4 line of FIG. 3), lower end-cap 46 has recessed portion64 for receiving one end of carbonaceous jacket 44. Lower end-cap 46further has positioned therein centering collar 66 dimensioned so as tofit into cavity 56 of carbonaceous jacket 44. Centering collar 66 aidsin centering carbonaceous jacket 44 in lower end-cap 46. Lower end-cap46 further houses lower seal 58 for aiding in complete sealing betweenlower end cap 46 and upper surface 76 (See FIG. 5) of base 14. Lower endcap 46 is further constructed with engagement ledge 60 for engagingthreaded shoulders 72 (See FIG. 5) of base 14.

The manner of engaging assembled filter cartridge 50, illustrated inFIG. 7, into base 14 of countertop filter unit 10 is shown in FIG. 5.Upper end-cap 52 of assembled filter cartridge 50 is inserted throughbase opening 70 from inferior base surface 68. Lower end-cap 46 issubsequently coupled to base 14 by engaging engagement ledge 60 alongengaging threaded shoulders 72 so as to affect axial translation of thefilter cartridge 50 relative to base 14. Preferably, once lower end-cap46 is rotated into its locked position, lower end-cap 46 will be flushwith base 14. Coupling may be through means of interlocking cammingsurfaces. Preferably, engagement is such that lower seal 58 is sealingengaged with respect to superior base surface 76. Preferablysimultaneous with coupling of lower end-cap 46 with base 14, upperend-cap 52 is also being sealing coupled to the internal surface ofinternal sump collar 78. Lower end-cap 46 may also be fabricated to haveslot 59 in its inferior surface to permit insertion of instruments intoslot 59 to ease turning of filter cartridge 50 and thus to engagecoupling.

Now referring to FIG. 6, there is shown a cross-sectional view of theassembled filter unit embodiment of FIG. 2. As illustrated, fluid entersthrough conduit 20 through inlet 28. Fluid circulates about carbonaceousfilter element 44 and under pressure crosses the walls of carbonaceouselement 44 entering into carbonaceous element cavity 56. Fluid incarbonaceous element cavity 56 is forced by pressure to exit throughhollow, microporous fiber bundle 48 and then through upper end cap neck62 to outlet 30, upper end cap neck 62 being sealingly connected to sumpoutlet sealing part 78 of sump 32. Outlet 30 is attached to conduit 18from which filtered water may be obtained. Microporous fiber bundle 48may be unhoused in cavity 56, or as illustrated, enclosed within ahousing, for example, cage 82, which preferably is perforated, and morepreferably disposed so as to permit exposure of more than 40% of thetotal surface area of the fiber bundle to the surrounding fluid.

While the invention has been described with respect to preferredembodiments, those skilled in the art will readily appreciate thatvarious changes and/or modifications can be made to the inventionwithout departing from the spirit or scope of the invention as definedby the appended claims.

What is claimed is:
 1. A method for fabricating a compound filtercartridge for filtering fluids comprising the steps of: a) providing acarbon block filter element having an outer surface and an innersurface, said carbon block filter element inner surface defining a voidapproximately concentric with a central axis of said carbon block filterelement, said carbon block filter element having sufficient permeabilityto permit passage of fluid from said outer surface through said innersurface of said carbon block filter element into said void and having ak-value of between 0.01 to about 0.10; b) providing a selectivelypermeable fiber bundle comprising a plurality of hollow, microporousfibers each having a first open end and a second open end an amultiplicity of pores along the surface thereof, wherein said first andsecond open-ends are potted in a sealing compound body such that saidfirst open end and said second open end of each of said hollow,microporous fibers are exposed on an outer end face of said sealingcompound body permitting fluid flowing radially toward said central axisand entering said hollow, microporous fibers to exit through said outerend face of said sealing compound body; c) positioning said selectivelypermeable fiber bundle in said void of said carbon block filter elementsuch that more than about 40% of the surface area of the selectivelypermeable fiber bundle is unsheathed from radial flows; and d) scalinglyconnecting said sealing compound body to said outer surface of saidcarbon block filter element.
 2. A method of according to claim 1,wherein the step of providing a selectively permeable fiber bundlecomprising a plurality of hollow, microporous fibers, further includesproviding hollow, microporous fibers with pores having a maximumdimension of about 0.20 microns.
 3. A method according to claim 2,wherein the step of providing a selectively permeable fiber bundlecomprising a plurality of hollow, microporous fibers, further includesproviding hollow, microporous fibers having pores forming tortuous,interconnected channels leading from one surface of the fiber to theother.
 4. A method according to claim 1, wherein the step of providing aselectively permeable fiber bundle comprising a plurality of hollow,microporous fibers, further includes providing hollow, microporousfibers having pores which permit the flow of fluids but block passage ofsub-micron particles and solutes.
 5. A method according to claim 1,wherein the step of providing a selectively permeable fiber bundlecomprising a plurality of hollow, microporous fibers each having a firstopen end and a second open end and a multiplicity of pores along thesurface thereof, wherein said first and second open-ends are potted in asealing compound body such that said first open end and said secondopen-ends of each of said hollow, microporous fibers are exposed on anouter end face of said scaling compound body permitting fluid flowingradially toward said central axis and entering said hollow, microporousfibers to exit through said outer end face of said sealing compoundbody, further includes providing a sealing compound body selected fromthe group consisting of: polyurethane, epoxy, polyethylene andpolypropylene.
 6. A method according to claim 1, wherein the step ofproviding a carbon block filter element having an outer surface and aninner surface, said carbon block filter element inner surface defining avoid approximately concentric with a central axis of said carbon blockfilter element, said carbon block filter element having sufficientpermeability to permit passage of fluid from said outer surface throughsaid inner surface of said carbon block filter element into said voidand having k-value if between about 0.01 to 0.10, further includesproviding a carbon block filter element defined at least in part by anextruded carbon block.
 7. A method according to claim 1, furthercomprising the step of positioning said selectively permeable fiberbundle in said void of said carbon block filter element such that morethan about 50% of the surface area of the selectively permeable fiberbundle is unsheathed from radial flow.
 8. A method according to claim 1,further comprising the step of positioning said selectively permeablefiber bundle in said void of said carbon block filter element such thatmore than about 75% of the surface area of the selectively permeablefiber bundle is unsheathed from radial flow.
 9. A method according toclaim 1, wherein the step of providing a carbon block filter elementhaving an outer surface and an inner surface, said carbon block filterelement inner surface defining a void approximately concentric with acentral axis of said carbon block filter element, said carbon blockfilter element having sufficient permeability to permit passage of fluidfrom said outer surface through said inner surface of said carbon blockfilter element into said void and having a k-value of between about 0.01to about 0.10, further includes providing a carbon block filter elementhaving a k-value of between about 0.02 to 0.07.
 10. A method accordingto claim 1, wherein the step of providing a carbon block filter elementhaving an outer surface and an inner surface, said carbon block filterelement inner surface defining a void approximately concentric with acentral axis of said carbon block filter element, said carbon blockfilter element having sufficient permeability to permit passage of fluidfrom said outer surface through said inner surface of said carbon blockfilter element into said void and having a k-value of between about 0.01to about 0.10, further includes providing a carbon block filter elementhaving a k-value of between about 0.03 to about 0.05.
 11. A method forfabricating a compound filter cartridge for filtering fluids comprisingthe steps of: a) providing a carbon block filter element having an outersurface and an inner surface, said carbon block filter element innersurface defining a void approximately concentric with a central axis ofsaid carbon block filter element, said carbon block filter elementhaving sufficient permeability to permit passage of fluid from saidouter surface through said inner surface of said carbon block filterelement into said void and having a k-value of between about 0.01 toabout 0.10; b) providing a cage structure configured to fit within saidcarbon block filter element void; c) positioning said cage structure insaid carbon block filter element void; d) providing a selectivelypermeable fiber bundle configured to fit within said cage structure,said selectively permeable fiber bundle comprising a plurality ofhollow, microporous fibers each having a first open end and a secondopen end and a multiplicity of pores along the surface thereof, at lestsaid first open-end being potted in a sealing compound body; and e)positioning said selectively permeable fiber bundle in said cagestructure and said scaling compound body anterior to said cage structureand said carbon block element, such that said first open end of saidhollow, microporous fibers is exposed on an outer end face of saidsealing compound body permitting fluid flowing radially toward saidcentral axis and entering said hollow, microporous fibers to exitthrough said outer end face of said sealing compound body, wherein saidcage structure has sufficient openwork such that more than about 40% ofthe surface area of said selectively permeable fiber bundle is inradial-flow contact with fluid when fluid fills said carbon block filterelement void.
 12. A method according to claim 11, wherein the step ofproviding a selectively permeable filter bundle comprising a pluralityof hollow, microporous fibers, further includes providing hollow,microporous fibers with pores having a maximum dimension of about 0.2microns. interconnected channels leading from one surface of the fiberto the other.
 13. A method according to claim 12, wherein step ofproviding a selectively permeable fiber bundle comprising a plurality ofhollow, microporous fibers, further includes providing hollow,microporous fibers having pores forming tortuous, interconnectedchannels leading from one surface of the fiber to the other.
 14. Amethod according to claim 11, wherein the step of providing aselectively permeable fiber bundle comprising a plurality of hollow,microporous fibers, further includes providing hollow, microporousfibers having pores which permit the flow of gases and vapors but blockpassage of sub-micron particles and solutes.
 15. A method according toclaim 11, wherein the step of providing a selectively permeable fiberbundle comprising a plurality of hollow, microporous fibers each havinga first open end and a second open end and a multiplicity of pores alongthe surface thereof, wherein said first and second open-ends are pottedin a sealing compound body such that said first open end and said secondopen end of each of said hollow, microporous fibers are exposed on anouter end face of said sealing compound body permitting fluid flowingradially toward said central axis and entering said hollow, microporousfibers to exit through said outer end face of said sealing compoundbody, further includes providing a sealing compound body selected fromthe group consisting of: polyurethane, epoxy, polyethylene andpolypropylene.
 16. A method according to claim 11, wherein the step ofproviding a carbon block filter element having an outer surface and aninner surface, said carbon block filter element inner surface defining avoid approximately concentric with a central axis of said carbon blockfilter element, said carbon block filter element having sufficientpermeability to permit passage of fluid from said outer surface throughsaid inner surface of said carbon block filter element into said voidand having a k-value of between about 0.01 to about 0.10, furtherincludes providing a carbon block filter element defined at least inpart by an extruded or molded carbon block.
 17. A method according toclaim 11, further comprising the step of positioning said selectivelypermeable fiber bundle in said cage structure and sealing compound bodyanterior to said cage structure and said carbon block element, such thatmore than about 50% of the surface area of the selectively permeablefiber bundle is in radial-flow contact with fluid flowing radiallytoward said central axis when said carbon filter element void is filledwith fluid.
 18. A method according to claim 11, further comprising thestep of positioning said selectively permeable fiber bundle in said cagestructure and sealing compound body anterior to said cage structure andsaid carbon block element, such that more than about 75% of the surfacearea of the selectively permeable fiber bundle is in radial-flow contactwith fluid flowing radially toward said central axis when said carbonfilter element void is filled with fluid.
 19. A method according toclaim 11, wherein the step of providing a carbon block filter elementhaving an outer surface and an inner surface, said carbon block filterelement inner surface defining a void approximately concentric with acentral axis of said carbon block filter element, said carbon blockfilter element having sufficient permeability to permit passage of fluidfrom said outer surface through said inner surface of said carbon blockfilter element into said void and having a k-value of between about 0.01to about 0.10, further includes providing a carbon block filter elementhaving k-value of between about 0.02 to about 0.07.
 20. A methodaccording to claim 11, wherein the step of providing a carbon blockfilter element having an outer surface and an inner surface, said carbonblock filter element inner surface defining a void approximatelyconcentric with a central axis of said carbon block filter element, saidcarbon block filter element having sufficient permeability to permitpassage of fluid from said outer surface through said inner surface ofsaid carbon block filter element into said void and having k-value ofbetween about 0.01 to about 0.10, further includes providing a carbonblock filter element having a k-value of between about 0.03 to about0.05.
 21. A method according to claim 11, further comprising the stepsof positioning a pre-filter on said carbon block filter element to coverthe outer surface of said carbon block filter element.
 22. A method forfabricating a compound filter cartridge for filtering fluids comprisingthe steps of: a) providing a pre-filter element for filtering courseparticulates configured so as to surround a void; b) providing a carbonblock filter element having a k-value of between about 0.01 to 0.10,said carbon block filter element configured to fit within saidpre-filter element void and defining a void approximately concentricwith a central axis of said carbon block filter element; c) positioningsaid carbon block filter element in said pre-filter element void; d)providing a selectively permeable fiber bundle configured to fit withinsaid carbon block filter element, said selectively permeable fiberbundle comprising a plurality of hollow, microporous fibers each havinga first open end and a second open end and a multiplicity of pores alongthe surface thereof, wherein said first and second open ends are pottedin a sealing compound body in such a manner that said first open end andsaid second open end of each of said hollow, microporous fibers areexposed on an outer end face of said sealing compound body permittingfluid entering said hollow, microporous fibers to exit through saidouter end face of said sealing compound body; and c) positioning saidselectively permeable fiber bundle in said carbon block filter elementvoid such that more than about 40% of the surface area of theselectively permeable fiber bundle is unsheathed from radial flow.
 23. Amethod according to claim 22, wherein the step of providing aselectively permeable fiber bundle comprising a plurality of hollow,microporous fibers, further includes providing hollow, microporousfibers with pores having a maximum dimension of about 0.20 microns. 24.A method according to claim 23, wherein the step of providing aselectively permeable fiber bundle comprising a plurality of hollow,microporous fibers, further includes providing hollow, microporousfibers having pores forming tortuous, interconnected channels leadingfrom one surface of the fiber to the other.
 25. A method according toclaim 22, further comprising the step of positioning said selectivelypermeable fiber bundle in said void of said carbon block filter elementsuch that more than about 50% of the surface area of the selectivelypermeable fiber bundle is unsheathed from radial flow.
 26. A methodaccording to claim 22, further comprising the step of positioning saidselectively permeable fiber bundle in said void of said carbon blockfilter element such that more than about 75% of the surface area of theselectively permeable fiber bundle is unsheathed from radial flow.
 27. Amethod according to claim 22, further comprising the step of positioningthe compound filter cartridge within a fluid filter unit having a filtercartridge receiving cavity, at lest one fluid inlet and at least onefluid outlet, wherein the compound filter cartridge is positioned in thefilter cartridge receiving cavity such that fluid from the at least onefluid inlet is exposed to the pre-filter element and fluid exitingthrough the outer end face of the sealing compound body is received bythe at least one fluid outlet.
 28. A method according to claim 27,further comprising the step of associating the at least one fluid inletwith an adaptor for providing fluid communication to the least one fluidinlet.
 29. A method according to claim 28, further comprising the stepof securing the adaptor to a fluid source.
 30. A method for fabricatinga filter cartridge for filtering fluids comprising the steps of: a)providing a carbon block filter element having opposed top and bottomends and an outer surface and an inner surface, said carbon block filterelement inner surface defining an axial cavity approximately concentricwith a central axis of said carbon block filter element, said carbonblock filter element having sufficient permeability to permit passage offluid from said outer surface through said inner surface of said carbonblock filter element into said axial cavity and having a k-value ofbetween about 0.01 to 0.10; b) providing a first end cap having a neckportion defining an axial passage and having a sealing member positionedon an outer periphery thereof; c) providing a second end cap defining abody portion having a recess formed therein for receiving the bottom endof the carbon block filter element and including a threadable engagementsurface positioned on the outer periphery thereof; d) securing saidfirst end cap to said top end of said carbon block filter element; ande) securing said second end cap to said bottom end of said carbon blockfilter element.
 31. A method according to claim 30, wherein the step ofproviding a carbon block filter element having an outer surface and aninner surface, said carbon block filter element inner surface definingan axial cavity approximately concentric with a central axis of saidcarbon block filter element, said carbon block filter element havingsufficient permeability to permit passage of fluid from said outersurface through said inner surface of said carbon block filter elementinto said axial cavity, further includes providing a carbon block filterelement having a k-value of between about 0.03 to about 0.05.
 32. Amethod according to claim 30, wherein the step of providing a carbonblock filter element having an outer surface and an inner surface, saidcarbon block filter element inner surface defining an axial cavityapproximately concentric with a central axis of said carbon block filterelement, said carbon block filter element having sufficient permeabilityto permit passage of fluid from said outer surface through said innersurface of said carbon block filter element into said axial cavity andhaving a k-value of between about 0.01 to about 0.10, further includesproviding a carbon block filter element having a k-value of betweenabout 0.02 to about 0.07.
 33. A method according to claim 30, furthercomprising the step of positioning the filter cartridge within a fluidfilter unit, the fluid filter unit having an elongated cavity forreceiving the filter cartridge and at least one fluid inlet, wherein thefilter cartridge is positioned in the elongated cavity such that fluidflow from the at least one fluid inlet is exposed to the outer surfaceof the carbon block filter element.
 34. A method according to claim 33,further comprising the step of securing the threadable engagementsurface to a corresponding threadable engagement surface defined on aportion of the elongated cavity.
 35. A method according to claim 33,further comprising the step of securing at least one outlet conduit forfluid from the axial passage on the first end cap.
 36. A methodaccording to claim 33, further comprising the step of connecting the atleast one fluid inlet with a fluid source.
 37. A method according toclaim 33, further comprising the step of connecting the at least onefluid inlet with an adaptor providing fluid communication between afluid source and the at least one fluid inlet.